The research presented herein is an analysis of acceleration measurements of the head during helmet-helmet impacts, where a player's helmet impacts another player's helmet, and with a youth population in football. This research is aimed at advancing current understanding of impact biomechanics for two specialized groups. The first study is an observational analysis focusing on helmet-helmet impacts, and the difference in effective mass and head acceleration measurements between the striking player and the struck player. The study involved working with football players outfitted with a sensor integrated into their helmets containing a 6 accelerometer array, capable of measuring linear accelerations and estimating angular accelerations. To evaluate helmet-helmet impacts, video analysis of past NCAA football competitions between Virginia Tech and University of North Carolina (UNC) were utilized to identify these impacts between instrumented players. A force balance was then carried out for the observed impacts and their respective acceleration measurements to compute the effective mass of the players. It was determined that the total mass recruited by the striking player was 28% to 77% more than that of the struck player. The second study focused on documenting the head impact biomechanics of a youth population. To accomplish this objective, unique accelerometer arrays, capable of measuring linear and angular accelerations, were integrated into existing youth football helmets for 7 players on a local team. Acceleration data were collected for every practice and game during the 2011 season to amass a total of 748 impacts. No instrumented player sustained a concussion during the 2011 season. Results of the study indicated impacts of greater magnitudes were more likely to occur in practices, and can be minimized by augmenting practice activities. / Master of Science

Shoulder-to-helmet (STH) impacts have been shown to cause approximately twenty percent of concussions in football, yet little research has investigated shoulder pad design and STH impacts. While shoulder pads are designed to protect the player wearing them, they have the potential to better protect the struck player in STH collisions. This study aimed to characterize STH impacts and identify the effect of shoulder pad stiffness on the struck head kinematics. Additional padding was added to a shoulder pad as means to reduce the overall stiffness of the system, and an unmodified shoulder pad acted as the control. Participants performed a series of impact tests with two shoulder pad variations to identify if additional padding in the shoulder pads could reduce head kinematics. Participants struck a helmeted Hybrid III dummy with a National Operating Committee on Standards for Athletic Equipment (NOCSAE) on the side, replicating a lateral STH impact. Linear and rotational kinematics of the struck head were recorded for each impact, and impact speed was derived from high-speed video. Peak kinematics were compared between shoulder pad configurations to identify differences in pad performance. Impact response corridors were developed from this study that could be used to inform future controlled laboratory test setups that replicate STH impacts. A controlled test setup would allow for future testing at higher impacts speeds to evaluate concussive level impacts. Overall, this study aimed to identify if shoulder pad design can affect the struck head kinematics in STH impacts, which would open a new avenue of player safety research and development. / Master of Science / Shoulder-to-helmet (STH) impacts have been shown to cause approximately twenty percent of concussions in football, yet little research has investigated shoulder pad design and STH impacts. While shoulder pads are designed to protect the player wearing them, they have the potential to better protect the struck player in STH collisions. This study aimed to characterize STH impacts and identify the effect of shoulder pad stiffness on the struck head kinematics. Participants performed a series of impact tests with two shoulder pad variations to identify if additional padding in the shoulder pads could reduce head kinematics. Participants struck the side of a crash test dummy head with their shoulder to replicate a STH impact. Linear and rotational kinematics were recorded for each impact, and impact speed was derived from high-speed video. Values that are used to quantify head injury were compared between shoulder pad configurations to identify differences in pad performance. This study defined impact response corridors that could be used to inform future controlled lab test setups that replicate STH impacts. A controlled test setup would allow for future testing at higher impacts speeds to evaluate concussive level impacts. Overall, this study aimed to identify if shoulder pad design can affect the struck head kinematics in STH impacts, which would open a new avenue of player safety research and development.

The plantar plate is a fibrocartilaginous tissue beneath the metatarsophalangeal joint (MTPJ). Plantar plate function centers around maintaining the static stability of the MTPJ, and its integrity facilitates the dynamic stabilizing functions of surrounding soft tissue structures. Injury to the plantar plate can cause significant forefoot discomfort focused around the MTPJ, swelling, and altered forefoot biomechanics from toe instability. Significant injury like either partial or complete tear of the plantar plate commonly requires surgical intervention to repair the tissue. As fibrocartilage, the plantar plate lacks an intrinsic capacity for robust healing, thus requiring a surgical repair aiming to restore proper function. Existing plantar plate repair techniques afford different perspectives for restoring plantar plate biomechanical function, though room for improvement exists for an enhanced repair. Our senior design team developed a novel approach for plantar plate repair using a two-piece snap fitting permanent implant. This novel technique was reduced to practice and required further experimental analysis of its functional capacity to inform future development. Two methodologies were used to evaluate the novel implant device designed for plantar plate repair. An implant isolated mechanical testing protocol was developed to evaluate the implant and suture construct of the repair in anatomically relevant orientations. A human cadaver tissue model protocol was employed to evaluate the integrity of the native plantar plate tissue, a simulated conventional repair, and our novel implant fixation repair. These methodologies used uniaxial tensile testing with custom test configurations to evaluate the structural integrity and properties of the implant-suture construct and simulated tissue only or tissue-repair constructs, respectively. Our results provided encouraging support for the use of mechanical testing and the continued development of this novel implant device for plantar plate repair. Additionally, qualitative outcomes from this testing revealed additional avenues to improve the novel implant device in support of further advancing the product for future use in the field of podiatric medicine. / Master of Science / The plantar plate is a soft, biological tissue that lies beneath the metatarsophalangeal joint (MTPJ), which comprises the ball of the foot. When injured, the plantar plate lacks capacity to fully heal the tissue, as its structural properties more closely resemble that of cartilage and ligaments, which also commonly fail to fully heal after injury. Due to the difficulties in facilitating healing and restoring its function, a plantar plate tear or rupture is commonly repaired surgically. Current methods for repairing a plantar plate tear vary, though room to enhance the overall surgical repair technique exists. Our senior design team developed a novel implant device for use in a modified surgical repair of the plantar plate, which aimed to improve upon the existing methods. This work focused on developing experimental methods to analyze and evaluate the function of this novel implant device that is relevant to the clinical application of plantar plate repairs. Two experimental setups were developed and used to analyze the function of our novel implant device. A simulated repair setup, relevant to the natural function of the plantar plate, was employed to evaluate the function of the implant and suture used in the repair. A human cadaver model experimental setup aimed to evaluate the plantar plate naturally, a conventional or existing repair, and our novel repair of a simulated torn plantar plate. The outcomes from these experiments encourage further exploration of implant product development as well as continued testing of this device in the future. Ultimately, this work has provided a foundation for the continued development of our novel implant device for plantar plate repair with the aim to bring this product to market and enhance the field of podiatric medicine.

The studies presented in this dissertation investigated biomechanical factors associated with sports-related brain injuries on the field and in the laboratory. In the first study, head impact exposure in youth football was observed using a helmet mounted accelerometer system to measure head kinematics. The results suggest that restriction on contact in practice at the youth level can translate into reduced head impact exposure over the course of a season. A second study investigated the effect of measurement error in the head impact kinematic data collected by the helmet mounted system have on subsequent analyses. The objective of this study was to characterize the propagation of random measurement error through data analyses by quantifying descriptive statistic uncertainties and biases for biomechanical datasets with random measurement error. For distribution analyses, uncertainties tend to decrease as sample sizes grow such that for a typical player, the uncertainties would be around 5% for peak linear acceleration and 10% for peak angular (rotational) acceleration. The third and fourth studies looked at comparisons between two headforms commonly used in athletic helmet testing, the Hybrid III and NOCSAE headforms. One study compared the headform shape, particularly looking at regions that are likely to affect helmet fit. Major differences were found at the nape of the neck and in the check/jaw regions that may contribute to difficulty with fitting a helmet to the Hybrid III headform. For the final study, the impact responses of the two headforms were compared. Both headforms were mounted on a Hybrid III neck and impacted at various magnitudes and locations that are representative of impacts observed on the football field. Some condition-specific differences in kinematic parameters were found between the two headforms though they tended to be small. Both headforms showed reasonable repeatability. / Ph. D.

Although cycling offers many health and environmental benefits, it is not an activity free of injury risk. Increases in cycling popularity in the United States over the past 15 years have been paralleled by a 120% growth in cycling-related hospital admissions, with injuries to the head among the most common and debilitating injuries. Bicycle helmets can reduce head injury risk and are presently required to meet safety standard certification criteria specifying a minimal level of acceptable impact protection. However, the conditions surrounding cyclist head impacts are thought to be much more complex than the test conditions prescribed in standards and have important implications related to mechanisms of injury. The overarching aim of this dissertation was thus to investigate the protective capabilities of bicycle helmets in the context of real-world impact conditions and relevant head injury mechanisms. This aim was achieved through a series of studies, the objectives of which were to: compare helmet impact performance across standards impact testing and more realistic, oblique impact testing; to probe how changing boundary conditions of oblique impact testing may influence helmet test outcomes; to use this knowledge to inform the development of an objective helmet evaluation protocol reflective of realistic impact conditions and related head injury risks; and finally, to enhance the body of knowledge pertaining to cyclist head impact conditions via advanced helmet damage reconstruction techniques. The compilation of results across these studies serves to enhance cyclist safety by stimulating improved helmet evaluation and design while simultaneously providing objective, biomechanical data to consumers, enabling them to make safety-based purchasing decisions. / Doctor of Philosophy / Although cycling offers many health and environmental benefits and is increasing in popularity in the United States, it is not always a perfectly safe activity. The number of cycling-related hospital admissions in the US has been increasing over the past 15 years. Cyclists often sustain head injuries from crashes, which can be particularly debilitating. Fortunately, wearing a helmet can protect against head injuries during a crash. Bicycle helmets are presently designed around safety standards that drop a helmeted dummy head onto a horizontal anvil and require the helmet to limit the force on the head to acceptable levels. However, standards tests overly simplify how cyclists actually hit their head during a crash and are consequently unable to assess how well helmets protect against common brain injuries like concussion. The overarching goal of this research was to evaluate how effectively bicycle helmets protect cyclists from concussion in realistic impact scenarios. Several studies were conducted to achieve this goal. Their individual objectives were to: compare how bicycle helmets reduce impact forces associated with standards tests versus more realistic, angled impact tests; to understand how changing constraints of an angled impact setup influences helmet effectiveness; to develop an unbiased evaluation protocol for bicycle helmets based on realistic cyclist crash scenarios and concussion risk assessment; and finally, to further explore how cyclists impact their head in real-world crashes using advanced techniques for reconstructing bicycle helmet damage from actual accidents. All of these studies lead to improved cyclist safety by stimulating improved helmet evaluation and design, while also providing consumers with information on how protective their helmets are.

When football originated in the 1800s, players wore no protective equipment. Between 1869 and 1905, there were 18 deaths and 159 serious injuries attributed to the sport. Following this, players began to wear protective equipment. The first use of a football helmet was in 1893, made of leather and designed to reduce the risk of skull fracture. Initially, football helmets were intended to protect a player against the most severe hits they would experience on the field. More recently, it has been shown that mild traumatic brain injuries, such as concussions, can induce long-term neurodegenerative processes. Since their introduction, helmets have transformed into plastic shells with padding designed to mitigate accelerations on the brain. With the growing concern for player safety, regulating bodies, like the National Operating Committee on Standards for Athletic Equipment, have implemented standards for protective equipment, including football helmets. On top of these standards, there have been multiple methods developed to assess helmet performance with different testing apparatuses. Manufacturers are interested in how their helmet performs according to multiple testing methods. This could be costly if they do not have the proper testing equipment that a protocol utilizes. This thesis assesses the interchangeability of different test equipment to reproduce a testing protocol. The desire to perform well in testing standards has driven the improvement of helmet performance and continued design innovation. The second aim of this thesis is to evaluate helmet performance and its relationship with design changes in football helmets manufactured between 1980 and 2018. / Master of Science / When football originated in the 1800s, players wore no protective equipment. Between 1869 and 1905, there were 18 deaths and 159 serious injuries attributed to the sport. Following this, players began to wear protective equipment. The first use of a football helmet was in 1893, made of leather and designed to reduce the risk of skull fracture. Initially, football helmets were intended to protect a player against the most severe hits they would experience on the field. More recently, it has been shown that mild traumatic brain injuries, such as concussions, can induce long-term neurodegenerative processes. Since their introduction, helmets have transformed into plastic shells with padding designed to mitigate accelerations on the brain. With the growing concern for player safety, regulating bodies, like the National Operating Committee on Standards for Athletic Equipment, have implemented standards for protective equipment, including football helmets. On top of these standards, there have been multiple methods developed to assess helmet performance with different testing apparatuses. Manufacturers are interested in how their helmet performs according to multiple testing methods. This could be costly if they do not have the proper testing equipment that a protocol utilizes. This thesis assesses the interchangeability of different test equipment to reproduce a testing protocol. The desire to perform well in testing standards has driven the improvement of helmet performance and continued design innovation. Another aim of this thesis is to evaluate helmet performance and its relationship with design changes in football helmets manufactured between 1980 and 2018.

Orb weavers intercept insects using non-hardening bioadhesive droplets, supported by two flagelliform fibers. Droplets contain an adhesive glycoprotein core and aqueous layer that confers hygroscopicity. The first study investigates the durability of these droplets to cycling, or repeatedly adhering, extending, and pulling off. Droplets of four species proved resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, thread adhesion is complex, relying on an integrated performance of multiple droplets and the flagelliform fibers. As insects struggle, the flagelliform fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets and dissipate the energy of struggling insects. Given this performance, the second study predicts that the material properties of both thread components have evolved in a complementary way. Comparative phylogenetics of 14 study species revealed that their elastic moduli are correlated, with glycoproteins being six times more elastic than flagelliform fibers. Spider mass affects the amount of each material, but not their properties. Since glycoprotein performance changes with humidity, we hypothesized that orb weavers generate greater adhesion at their foraging humidity. After delimiting low and high humidity species groups (eight and six species, respectively), bridge force was determined as total contributing droplet adhesion at three humidities. Only three spiders generated greater adhesion outside of their foraging humidity. The distribution of force along a suspension bridge differed from a previously reported pattern. We also characterize the sheet configuration, which generates force similar to suspension bridges. / Master of Science / In nature, adhesives are used for a variety of functions. Many animals use adhesives use adhesives when climbing. Examples include toe pads of geckos, tarsal pads of ants, and tube feet of and sea urchins. Here, adhesion is repeatedly generated and released as the animal moves. However, some animals depend on permanent adhesives to anchor to surfaces. Marine mussels and barnacles, whose adult forms are sessile, use adhesives to resist the powerful action of waves and currents. Adhesion also plays a critical role in prey capture, where it prevents prey from escaping. The sticky droplets of a sundew plants and the adhesive capture threads of spider orb webs trap flies. Biologists and engineers study these bioadiehsives in search of inspiration and principles that will guide the development of new materials, including adhesives that function underwater, harden rapidly, or remaining pliable after adhering. This study investigated the material properties of capture threads spun by orb weaving spiders, which rely on non-hardening sticky droplets, supported by two protein fibers to capture insects. Inside each droplet is an adhesive core allows droplets to adhere to an insect and to extend as it struggles to escape. Surrounding this core is an aqueous layer that attracts atmospheric water, causing droplets to track changes in ambient humidity. A study of the cycling (or reusability) of four species' droplets repeatedly adhered a droplet to a surface and extending it to pull-off. These droplets were very resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, prey capture is more complex, relying on the integration of multiple droplets and their supporting flagelliform fibers. As insects struggle, these fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets to resist an insect escape. The threads of 14 species were examined to test the hypothesis that material properties of both thread components have evolved in a complementary way to optimize adhesive performance. This revealed that the elasticities of the two capture thread components were correlated, with support fiber elasticity being greater. Capture threads generated the greatest adhesion at humidities during times that a spider feeds, although the distribution of this force across a suspension bridge showed different patterns among the species. The functional integration of a capture thread's components and its ability to respond to environmental humidity gives it exciting biomimicry potential.

Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury. / Master of Science / Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.

The objectives of these two studies were to characterize normal growth and resultant changes in conformation and walk kinematics of warmblood foals. The first study quantified linear and angular conformation changes of 13 warmblood foals during the first 9 mo of growth. An objective photographic method of evaluating conformation was used to obtain all data. All linear measurements increased significantly over the investigated ages and growth rates were highest in the first 2 mo of growth. Total percentage of growth during the study was greatest for neck and back length. Distal limb growth was minimal over the investigated ages. Metacarpal growth slowed earlier than many other traits. Length of the metatarsus increased minimally during the studied ages with significant growth occurring only between 23 wk and post-weaning measurements. Increasing wither heights were positively associated with increases in scapula, humerus, radius, ilium, femur, tibia and metatarsal and metacarpal lengths. Angular conformation also changed significantly during growth. Trends in angular changes were generally less clear than those for linear variables. Scapula, femur and hock angles significantly increased and humerus angle decreased with age. Utilizing a plumb line from the hock upward, the distance of the hindlimb behind the body was quantified. The distance out behind decreased significantly between 1 and 15 wk. Distance out behind was positively correlated with tibia angle at all ages. The second study quantified linear and temporal kinematics of the walk in growing foals. Nine warmblood foals from the first study were filmed as they walked over a uniform concrete surface covered in 13mm thick rubber matting. Speed was controlled through the use of a uniform handler with a metronome. Trait means at ages 3, 11, 21 wk and post-weaning were compared. Length variables were standardized to percent of total stride length. Temporal variables were standardized to percent of stride duration. Stride length and duration increased significantly with age. Step lengths, stance duration and protraction and retraction durations did not change across ages. Over-stride decreased significantly with age, potentially due to increased back length in older foals. Linear distance between diagonal hooves during stance increased with age, and was negatively correlated to the decrease in over-stride. While older foals appeared to display a more regular, 4-beat walk rhythm, timing between lateral and diagonal footfalls remained significantly different at all ages. Both conformation and kinematics changed during growth. Characterizing conformational changes due to growth can allow a better understanding of how foal conformation and gait change during growth and may predict these traits in adults, thus allowing selection of top performance prospects at a younger age. / Master of Science

No description available.